"One of the bombers detonated an IED (improvised explosive device) strapped to her body within Biu's main market, while the other one detonated outside the market square," the spokesman said.

The police said 13 people were killed, while a spokesman for a local civilian militia, Ibrahim Saidu Maniya, said the death toll was as high as 18.

No one has claimed responsibility for the attack, but the Boko Haram group, led by Abubakar Shekau, has previously used women and adolescent suicide bombers to carry out attacks in the area.

"They were powerful blasts which were heard all over the town," Biu resident Ahmad Babagana, who lost a friend in the attack, told AFP.

"I heard huge blasts that came in succession and saw plumes of black smoke coming from the direction of the market," said another resident, Zakari Tiko.

"I instantly knew the market had been attacked," Tiko said.

Biu and neighbouring villages have been repeatedly hit by suicide and bomb attacks blamed on Boko Haram over the last eight years. In August 2015, a suicide bomber killed at least 50 people at a market in a nearby village.

Despite increased military success in the fight to dislodge Boko Haram, the group continues to launch deadly attacks in the country.

At least 20,000 people have been killed and more than 2.6 million others made homeless in its quest to establish a hardline Islamic state in northeast Nigeria